Velocity-modulated electrondischarge device



March 22, 1949. B Q GARDNER 2,464,801

VELOCITY MODULATED ELECTRON-DISCHARGE DEVICE Filed` April 25, ,1945

F/G/l A /20 'y -lxllff- Patented Maezz, 1949 l VELOCITY-MODULATEDELECTRON- DISCHARGE DEVICE Bernard C. Gardner, Waltham, Mass., assignorto Raytheon Manufacturing Company, Newton, Mass., a corporation ofDelaware Application April 23, 1946, Serial No. 664,209

6 Claims. 1

This invention relates to electron-discharge devices, and moreparticularly to electron-discharge devices of the velocity-modulatedtype, commonly known as reflex Klystrons.

It is desirable that devices of the general character indicated lendthemselves to a variety of operating conditions which require differentdistances of penetration oi their electron beams into the retardingelectric fields thereof. In other words, it is desirable that suchdevices operate efficiently over a wide range of frequencies.

Where space is at a premium in electron-discharge devices of the type towhich reference has been made, the above-mentioned results can beobtained only over a limited range of operating conditions,corresponding to a relatively narrow band of frequencies. Attempts tooperate outside this limited range result in greatly decreased output.

It is, therefore, the main object of the present invention to provide arelatively small electrondischarge device of the reflex Klystron typewhich is capable of eihcient operation over a relatively wide range offrequencies.

It is a further object of the present invention to accomplish theforegoing in a simple and inexpensive manner.

These, and other objects of the present invention, which will becomemore apparent as the detailed description thereof progresses, areattained, brieiiy, in the following manner:

The device includes an electron gun, a pair of grids spaced from saidgun and adapted to be connected, respectively', to the oppositeterminals oi a tuned circuit, and a repeller electrode spaced from saidgrids and adapted to have a retarding electric field established betweenitself and said gun. In such a device, the shape of the retarding fieldis generally such that the transit time for electrons approaching therepeller electrode at different angles varies considerably, especially,where the penetration of the eld is intended to be large, as at the thelow-frequency end of the band over which it is desired to operate. Thisis caused by the shielding effect of portions of said repeller electrodeupon other portions thereof. This varying transit time causesinefficient electron bunching for any given eld intensity with aconsequent loss of power.

In accordance with the present invention, the repeller electrode isprovided with means, for example, a perforate wall, extending therefromin the direction oi the retarding iield, for eliminating the abovereferred to shielding effect and so shaping said eld as to cause thesame to be composed of substantially parallel lamellae which areequipotential over areas substantially coextensive with the surface ofsaid repeller electrode. Under these conditions, substantially all ofthe electrons entering the retarding eld penetrate the same to likeextent regardless of the angles at which they approach the repellerelectrode. Consequently, they all have substantially the same transittime for any given eld inten-I sity, and efficient bunching andincreased power result over a relatively wide frequency band.

In the accompany specification there shall be described, and in theannexed drawing shown, two illustrative embodiments of theelectron-discharge devices of the present invention. It is, however, tobe clearly understood that the present invention is not to be limited tothe details hereinshown and described for purposes of illustration only,inasmuch as changes therein may be made without the exercise ofinvention, and within the true spirit and scope of the claims heretoappended.

In said drawing:

Fig. 1 is a longitudinal sectional view taken through the center of anelectron-discharge device incorporating the principles of the presentinvention.

Fig. 2 is a similar, enlarged View of one form of repeller electrodewhich may be utilized in said device; and

Fig. 3 is a view similar to Fig. 2 of another form of repeller electrodewhich may be utilized to obtain like results.

Referring now more in detail to the present invention, with particularreference to the illustrative embodiment thereof shown in Figs. 1 and 2of the drawing, the numeral I0 generally designates anelectron-discharge device of the velocity-modulated type, known as aKlystron, more especially, a reflex Klystron,

As is well known, in a device of this type, a beam of electrons is actedupon by an alternating voltage to cause some of said electrons to beaccelerated and others to be decelerated. By permitting the electrons soacted upon to thereafter drift, the accelerated electrons overtake thosewhich were decelerated, resulting in a beam in which bunches ofelectrons are spaced by regions in which there are relatively fewelectrons. The beam thus velocity modulated is caused to act upon aresonant circuit and give up thereto the energy represented by themodulation. In the reflex. Klystron, a single resonant circuit modulatesthe electron beam and, subsequently, is energized thereby, the beam,after passing the resonant circuit a rst time and becoming velocitymodulated, being caused by an appropriate electric eld to substantiallyretrace its path and pass by the resonant circuit a second time toenergize the same. l

In the device under consideration, the electron beam is obtained from agun, which may consist of a suitably coated cathode Il, heated, by afilament l2, to a temperature resulting in copious electron emission,and surrounded by an accel- 3 erating electrode. I3. said cathode II andelectrode I3l being supported, for example, from a reentrant press, notshown, formed in the bottom of an evacuated glass envelope I4 mountedupon a base I5. The beam thus obtained passes through a pair of spacedgrid structures IS andv I1 which may be supported as by being sealedthrough the Walls of the envelope I 4, said grid structures beingconnected, externally of the device, to any desired tuned circuit, asherein shown, respectively, to the outer and inner conductors I8 and I9of a coaxial cavity resonator from which power may be extracted by meansof a coupling loop 20'. The cavity resonator 2l) is secured to the tubeportions of the device by means of the interengaged supporting membersI8 and I9'.

Spaced from the grid structures I6 and I'I, and supported, for example,from a lead-in conductor 2| passing through the inner conductor I9 ofthe coaxial cavity resonator 2, and entering the envelope Id through aglass bead 22 in the grid structure I'I, is a repeller electrode 23which, when supplied with a suitable potential, causes the electron beamapproaching the same after having passed through the grids to turn aboutand reapproach said grids.

Such a repeller electrode is generally in the form of a shallowdish-like member which, because of its shallowness, permits penetrationof the electron beam only over a limited range. Greater range ofpenetration can be obtained by making the repeller electrode deeper, butthen the retarding field is caused to have the shape indicated by thebroken line A in Fig. 2 of the drawing. This shape is the result of theshielding of the corner portions of the repeller electrode by the flangeportion thereof. It will be apparent that electrons entering such afield and approaching such a repeller electrode at different an-glespenetrate said field to different distances before retracing theirpaths, as a result of which the above-referred to ineflicient bunchingtakes place.

However, in the present invention, this disadvantage is overcome bydistorting the field indicated by the broken line A in Fig. 2 so as tocause the same to be composed of substantially parallel lamellae whichare equipotential over areas substantially coextensive with the repellera electrode surface, as indicated by the full lines B, C and D in saidFig. 2. This is accomplished by securing about the periphery of therepeller electrode a perforate Wall, for example, a plurality ofuniformly spaced -conductive rods 24 which, as here shown, lie in thesurface of a cylinder projecting at right angles to the surface of saidrepeller electrode. Such a wall deepens the electrode so as to permit aWide range of electron beam penetration and at the same time destroysthe above-mentioned shielding of the corners of the electrode. With thefield thus shaped, Substantially all of the electrons entering the samepenetrate to like distances for any given eld intensity, and thereforehave substantially similar transit times. Eiicient bunching results overa wide range of frequencies, and a much more useful tube is therebyobtained.

Instead of employing the multiplicity of rods 24 shown in Figs. 1 and 2of the drawing, a similar result can be produced by supporting, from afew relatively separated rods 25 extending from the periphery of therepeller electrode 23, a spiral conductive member 26 the turns of whichmay be equally or unequally spaced from each other, depending upon theexact shape of field desired, and, as here shown, lying in the surfaceof a cylinder projecting at right angles to the surface of said repellerelectrode. Such a construction is shown in Fig. 3 of the drawing. Whilethe spacing of the turns of the spiral member 26 decreases from top tobottom as here'illustrated, it is to be understood that other forms ofunequal spacing or, as stated, equal spacing can be employed.

This completes the description of the aforesaid illustrative embodimentsof the present invention. It will be noted from all of the foregoingthat the present invention provides simple and inexpensive means for soshaping the retardlng eld of a reflex Klystron as to enable efllclentelectron bunching over a wide range of frequencies.

Other objects and advantages of the present invention will readily occurto those skilled in the art to which the same relates.

What is claimed is:

1. A repeller electrode for an electron-discharge device of the reiiexKlystron type comprising a plurality of conductive members disposedabout the periphery of said repeller elec trode, and projectingsubstantially at right an gles to the surface thereof.

2. A repeller electrode for an electron-discharge device of the reexKlystron type comprising a plurality of uniformly spaced conductive rodsdisposed about the periphery of said repeller electrode, and projectingsubstantially at right angles to the surface thereof.

3. A repeller electrode for an electron-dis-v charge device of thereflex Klystron typel comprising a spiral conductive member the turns ofwhich lie in the surface of a cylinder projecting at right angles to thesurface of said repeller electrode.

4. A repeller electrode for an electron-discharge device of the reflexKlystron type comprising a spiral conductive member the turns of whichare unequally spa-ced from each other and lie in the surface of acylinder projecting at right angles to the surfaces of said repellerelectrode.

5. A repeller electrode for an electron-dls charge device or the reflexKlystron type comprising a dish-shaped member having a bottom wallextending substantially transverse to the direction of the retardingelectric eld of said device, and a perforated side Wall extending fromsaid bottom Wall substantially parallel to the direction of saidelectric field.

6. A repeller electrode for an electron-discharge device of the reflexKlystron type comprising a cylindrical member open at one end and closedat the other, the portion of said memI ber lying in the surface of acylinder being perforated.

BERNARD C. GARDNER.`

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,411,913 Pierce et al. Dec. 3,1946 2,429,243 Snow et al. -.-.w-.ee Oct. 2,1. 184'(

